Using Enthesis Robusticity to Infer Activity in the Past: A Review

In bioarchaeological studies, entheseal change is commonly used to infer patterns of activity in past populations. This category of skeletal modification includes both pathological changes (enthesopathies) and changes in size, shape and surface complexity (robusticity). Despite the recent impetus to reassess the use of enthesopathies as markers of activity, robusticity has received little critical attention. In this review, we reassess key assumptions that underpin the use of robusticity in activity studies, drawing on anatomical, physiological, biomechanical and sports medicine literature sources. We find that, whilst there is some evidence to support the assumption that variation in enthesis robusticity reflects different activity patterns, little is known about the process through which this variation is produced. Presently, the stimuli (dynamics of muscle use or muscle size) for entheseal adaptation are ill-defined, a situation that limits our interpretive abilities. Consideration of bone functional adaptation principles and of the relationship of entheses to soft tissue also highlights how other factors, such as age, sex and genetic background, may influence enthesis robusticity and obscure activity-related adaptation. Understanding how these factors influence enthesis robusticity helps define how robusticity studies should be controlled, but further research is required to clarify how these factors interact with activity in robusticity development and the precise relationship between activity and robusticity. Ultimately, this review emphasises the complexity of entheseal structures and their morphological development. Any interpretation of activity from enthesis robusticity should be approached with caution, but in some circumstances, the endeavour may be ill-advised.